Organic photoreceptors (OPCs) have the following advantages over other photoreceptors:
(1) good optical properties such that the light absorption wavelength range is wide, and light absorbance is high;
(2) good electric properties such that the optical sensitivity is high, and the charge property is stable;
(3) wide material selectivity such that the constituents thereof can be selected from various materials;
(4) good productivity;
(5) low costs; and
(6) low toxicity.
Therefore, organic photoreceptors have been broadly used for copiers, facsimiles, printers, and multifunctional products having two or more of copying, facsimileing and printing functions.
Recently, a need exists for miniaturized image forming apparatus, and the size of image forming apparatus becomes smaller and smaller. Therefore, the diameter of the photoreceptors used for such image forming apparatus also becomes smaller and smaller. In addition, since a need exists for high speed and maintenance-free image forming apparatus, photoreceptors having good durability are desired. Specifically, a need exists for a photoreceptor, which has a good combination of abrasion resistance, scratch resistance and electric property and which can produce high quality images over a long period of time. It is known that a protective layer including a filler or a protective layer crosslinked by light or heat is used as an outermost layer of a photoreceptor to enhance the abrasion resistance and scratch resistance of the photoreceptor. In addition, the material used for a substrate of a photoreceptor preferably has good mechanical strength to prevent occurrence of a problem (scratch/indentation problem) in that scratch or indentation is formed on the substrate in a photoreceptor production process or a maintenance operation of the photoreceptor due to handling errors. At the present time, aluminum alloys have been broadly used for substrates of photoreceptors because of having light weight and high electroconductivity while having a good combination of mechanical strength and processability.
However, substrates made of such an aluminum alloy tend to easily cause the above-mentioned scratch/indentation problem and form dent. In addition, substrates preferably have good dimension stability to stably produce high quality images. Therefore, precision machining (such as precision cutting of surface of such substrates) is preferably performed on the substrates. In this case, the production costs of the substrates increase. In addition, manufacturing such aluminum alloys takes a huge amount of energy, and therefore the amount of emitted CO2 is very large. Recently, from the environmental viewpoint, reduction of CO2 emission is desired. Therefore, it is preferable to produce a substrate while reducing CO2 emission. In attempting to solve the problems of such aluminum alloys, electroconductive resin substrates have been proposed. Such resin substrates have a light weight, and in addition by including a filler therein, a good mechanical strength can be imparted thereto, thereby making it possible to produce a substrate for photoreceptors, which has good resistance to scratch, indentation and dent. In addition, since manufacturing such resin substrates dramatically reduces CO2 emission, the resin substrates are environmentally friendly.
Until now, various types of resin substrates have been disclosed, and examples thereof are as follows.
(1) Resin substrates prepared by molding an electroconductive resin including a thermoplastic resin such as polyamides and polyesters, and an electroconductive agent such as carbon black dispersed in the thermoplastic resin;
(2) A resin substrate prepared by molding an electroconductive resin including a thermosetting resin such as phenolic resins, and an electroconductive agent such as carbon black dispersed in the thermosetting resin.
(3) A resin substrate for which a crosslinkable phenolic resin is used as a main component and in which a carbon black is dispersed, wherein the substrate has an outermost layer having a resistance of not higher than 5×105Ω, and wherein the purpose is to improve surface smoothness, electric properties, adhesion to photosensitive layers, and resistance to solvents and scratch.(4) A resin substrate for which a resol-type phenolic resin is used as a main component, wherein the purpose is to provide a substrate having a light weight, and a good combination of electroconductivity, nonmagnetism, heat resistance and dimension stability.(5) A resin substrate for which a polyamide resin prepared from metaxylylene diamine and adipic acid is used, wherein the purpose is to provide a substrate having a good combination of heat resistance, chemical resistance and mechanical strength.(6) A resin substrate for which a polyester resin is used, wherein the purpose is to provide a substrate having good dimension stability even under high temperature and high humidity conditions.(7) A resin substrate for which a mixture of a polyester resin and a polycarbonate resin is used, wherein the purpose is to provide a substrate having a good combination of chemical resistance, moldability, dimension stability, and adhesion to photosensitive layers.